ROOM-TEMPERATURE LOW-CYCLE FATIGUE BEHAVIOR OF TI-27AL-15NB ALLOY

Low-cycle fatigue (LCF) behaviour of the alloy Ti-27Al-15Nb, in (alpha(2) + B2) heattreated condition was studied in total axial strain control mode at different total strain amplitudes (Delta epsilon(t)/2) from +/- 0.65 to +/- 1.0% and room temperature. While there was little hardening of the material at the lowest strain amplitude (Delta epsilon(t)/2:+/- 0.65%), pronounced hardening was observed at the higher strain amplitudes (Delta epsilon t/2 greater than or equal to 0.83%). The cyclic stress, at high strain amplitudes, continuously increased from the beginning till fracture of the specimens. The LCF resistance of the material was found to be low and this was due to its poor ductility at room temperature. Dual slope was observed in the Coffin-Manson plot, with less slope of the upper segment than that of the lower one, as observed in several alloys. The fracture behaviour pointed to brittleness and faceted features were observed.